Electronic tube element protective coating



June 12, 1956 E. TENO 2,750,528

ELECTRONIC TUBE ELEMENT PROTECTIVE COATING Filed Feb. 1'7, 1955 STIFFENING l4 COATING OVER GRID SURFACE l4 (COATING) INVENTOR E D WA R D T E NO W/ ATTORNEY ELECTRONIC TE ELEMENT PROTECTIVE COATING Edward Teno, Emporium, Pa., assignor to Sylvania Electrio Products Inc., a corporation of Massachusetts Application February 17, 1955, Serial No. 488,987

Claims. (Cl. 313-350) This invention relates to electron discharge devices, and more particularly to the electrodes for such devices, and the methods for processing and mounting these electrodes.

Heretofore, grids for electron discharge tubes of the type comprising side rods having lateral wires wound thereon were formed on grid making machines, subsequently degreased to remove contaminants, and then stored within packaged trays. These trays have individual compartments for each grid, so that the lateral wires of the grid will not become deformed or jammed by contact with other grids. When the grids were ready for the mounting operation, the operator removed the package from about the trays, picked up the grids by means of tweezers, and subsequently placed them upon mounts by threading each of them over a cathode or over another grid, depending on the type of tube. During this threading step, the lateral wires of the grid often became deformed through contact with other electrodes already mounted, and had to be replaced. This inefiicient, costly, and detailed process of cleaning, storing and mounting grids was necessitated by the inherent flimsiness of these grids and their susceptibility to contamination. In addition, it was often difficult in production to observe defects of the grid lateral wire alignment, and losses due to misalignment caused by handling and assembly operations were very often not discovered until the electron discharge tube had been completely processed, and was being tested for electrical characteristics. Losses due to jammed and misaligned lateral wires result in such rejects as are caused by short circuits between elements, high grid and plate currents, poor cut-01f, and noise. Contaminated grids could cause low emission.

Accordingly, it is an object of this invention to provide for an electrode which, during processing, will be strong, rigid, an non-contaminable.

Another object of this invention is the provision of a grid which will be rigid and remain in a non-contaminable state until the mounted assembly has been completed.

A further object is the provision of an improved method of manufacturing electron tubes whereby an electrode is maintained in a rigid and non-contaminable state until the last steps in the processing of the tube are reached.

A further object of this invention is the provision of an improved method of processing electrodes for electron discharge tubes.

It is a still further object of this invention to provide for an improved electron discharge device.

The foregoing objects are achieved by providing an electrode, here exemplified as a grid, with a coating subsequent to the steps of forming and cleaning the grid. This coating, applied in liquid form, quickly dries and thereby stiffens and rigidifies the grid to facilitate handling. The coating may be removed either before or during the processing of the electron tube.

For a better understanding of the invention reference is made to the following detailed description and accompanying drawing in which Fig. 1 is a plan view of a frag- "nited States Patent 0 Ice A 2,750,528

Patented June 12, 1956 mentary portion of a coated grid, with the thickness of the coating greatly exaggerated.

Fig. 2 is a top view thereof.

After a grid for an electron discharge tube has been made, such as the conventional grid shown in the drawing, and which grid may comprise a pair of side rods 10 with a grid lateral Winding 12 thereon, a protective coating 14 is applied to it in any conventional manner, as by dipping, spraying or running a stream of coating material over the grid. The means for coating the grid would be dependent upon the coating thickness desired, the use of and position of the grid within the electrode assembly, the number of turns per inch of the lateral wires, and the amount of area to be covered. The coating material should be of a composition which may be readily and easily removed. Numerous coatings have been successfully used as the electrode protective coating, such as lacquers, an example of which is ethyl methacrylate with acetone, diethyl carbonate, or Pent-acetate as thinners. Following the coating operation, a fast drying is accomplished by the application of a controlled heat by any conventional means such as an oven, electric heater, or radiant heater. In order to provide for a fast drying operation, which is essential in high speed production, the quick drying or thinning agents previously enumerated may be utilized. This coating and these drying agents do not leave a residue which would affect the performance of the tube.

The electrode produced by the coating and drying operations is stiff and rigid, and the grid wire is not contaminatable, since the coating adheres to the side rods and lateral wires of the grid. The coating may be applied so as to completely cover the grid like a sheath, thereby forming an imperforate tubular member. If half-grids are employed, a solid imperforate wall would be formed. The solidified coating material between the lateral wires provides primarily for the maintenance of constant spacing of these wires. When grids with a small number of lateral wire turns per inch are employed, or when it is otherwise so preferred, it may be advisable to coat the grid so that the coating surrounds only the side rods and lateral wires, but does not span the area between the lateral wires. The stiffness of this type of coated grid is derived from the additional support of the lateral wires at the juncture point with the side rods, and the additional rigidity of the lateral wires by virtue of the dried coating When production methods do not necessitate completely protectively covering the grid, it may be coated over those areas most susceptible to lateral wire mutilation and contamination.

The coated grid, after being mounted and enclosed within the confines of the anode electrode, is treated for removal of the coating. Several methods may be uitilized for removing the coating, such as by washing with lacquer solvents, or by heating the coating in a reducing or oxidizing atmosphere or, if desired, in a partial vacuum. Heating the lacquer coating while the electron discharge tube is being processed under vacuum is particularly adaptable for automatic production. The heat depolymerizes the coating into a gaseous monomer.

It is apparent that the method of handling grid electrodes described greatly reduces previous production losses due to inherent frailty of the grids. In addition, it obviates the necessity of careful packaging to prevent contamination of the grids from such foreign matter as lint, dust, corrosion, and rust.

Although only one embodiment of the invention has been described, it is to be understood that other modifications may be made within the scope of this invention. For example, any electrode for an electron discharge device, such as anodes, shields, terminal members, confining plates,

and so forth, which must be handled and which may be flimsy in character or subject to contamination may be treated in the manner previously described. In addition, the composition for the protective coating and the methods of applying and removing the coating were recited only by way of example, since many other compositions and methods will be apparent to one having ordinary skill in the art.

What I claim is:

1. A grid assembly for an electron discharge device comprising a grid electrode having lateral wires supported by side rods, and a removable solidified protective coating covering said side rods and lateral wires.

2. A grid assembly for an electron discharge device comprising a grid electrode having lateral wires supported by side rods, and a removable solidified protective coating at least partially covering said side rods and lateral wires.

3. A grid assembly for an electron discharge device comprising a grid electrode having lateral wires supported by side rods, and a lacquer coating at least partially covering said side rods and lateral wires.

4. A grid assembly for an electron discharge device comprising a grid electrode having lateral wires supported by side rods, and a removable solidified protective coating covering said side rods and lateral wires, the protective coating extending between said lateral wires to form an imperforate assembly.

5. A grid assembly for an electron discharge device comprising a grid electrode having lateral wires supported by side rods, and a removable solidified protective coating covering said side rods and lateral wires, the protective coating extending between said lateral wires to form an imperforate tubular assembly.

6. A grid assembly for an electron discharge device comprising a grid electrode having lateral wires supported by side rods, and a removable solidified protective lacquer coating covering said side rods and lateral wires, the lacquer coating extending between said lateral wires to form an imperforate assembly.

7. A grid assembly for an electron discharge device comprising a grid electrode having lateral wires supported by side rods, and a. removable solidified protective lacquer coating covering said side rods and lateral wires, the lacquer coating extending between said lateral wires to form an imperforate tubular assembly.

8. A grid assembly for an electron discharge device comprising a grid electrode having lateral wires supported by side rods, and a removable solidified protective coating of ethyl methacrylate covering said side rods and lateral wires.

9. In the manufacture of electron discharge devices, the method of processing a grid electrode having lateral wires supported by side rods, comprising the steps of applying a protective coating to the grid and side rods, drying and solidifying said coating to form a rigid subassembly, mounting the coated grid in association with the remainder of the discharge device assembly, and subsequently removing said coating.

10. In the manufacture of electron discharge devices, the method of processing a grid electrode having lateral wires supported upon side rods, comprising the steps of applying a protective coating to the grid so that the coating extends from one lateral wire to another and over the side rods, drying and solidifying said coating to form a rigid sub-assembly, mounting the coated grid in association with the remainder of the discharge device assembly, and subsequently removing said coating.

References Cited in the file of this patent UNITED STATES PATENTS 1,209,247 Bastian Dec. 19, 1916 1,931,874 Mendenhall Oct. 24, 1933 2,413,731 Samuel Jan. 7, 1947 2,453,753 Loosjes Nov. 16, 1948 2,572,055 Saldarini Oct. 23, 1951 

1. A GRID ASSEMBLY FOR AN ELECTRON DISCHARGE DEVICE COMPRISING A GRID ELECTRODE HAVING LATERAL WIRES SUPPORTED BY SIDE RODS, AND A REMOVABLE SOLIDIFIED PROTECTIVE COATING COVERING SAID SIDE RODS AND LATERAL WIRES. 